1. Field of the Invention
This invention relates to lubricant additives and compositions thereof and, more particularly, to lubricant compositions comprising oils of lubricating viscosity or greases prepared therefrom containing a minor friction reducing amount of a borated sorbitan ester.
2. Description of the Prior Art
Many means have been employed to reduce overall friction in modern engines, particularly automobile engines. The primary reasons are to reduce engine wear thereby prolonging engine life and to reduce the amount of fuel consumed by the engine thereby reducing the engine's energy requirements or fuel consumption.
Many of the solutions to reducing fuel consumption have been strictly mechanical, as for example, setting the engines for a leaner burn or building smaller cars and smaller engines. However, considerable work has been done with lubricating oils, mineral and synthetic, to enhance their friction properties by modifying them with friction reducing additives.
Hydroxyesters are known for their friction reducing properties when added to lubricant fluids. However, these hydroxyesters have not found widespread use in many applications because of their inherent inability to control bearing corrosion; it is believed that the poor control of bearing corrosivity of these hydroxyesters is due to the presence of reactive hydroxyl groups. Borated sorbitan esters are better friction reducers than their unborated counterparts and also reduce bearing corrosion to minimal, acceptable levels. It is believed that the conversion of hydroxyl groups to borate esters groups leads to these multiple performance improvements. These borated sorbitan esters to the best of applicant's knowledge and belief are novel and have not been used as friction reducing additives or as anticorrosion or antioxidant additives in lubricating compositions.
The closest prior art known by applicants is exemplified by: U.S. Pat. No. 3,533,945, concerning borated esteralkenyl succinic acid ester of a polyhydric alcohol; U.S. Pat. No. 3,544,614 to complex esters from dibasic acids, polyhydric alcohols and monobasic acid, one polyhydric alcohol being sorbitol; U.S. Pat. No. 3,772,357 teaching, among other things, the product of reaction between sorbitan monolaurate and trimethyl borate; and U.S. Pat. No. 4,034,038 to lubricant compositions containing a product made by reacting, e.g., sorbital, with a succinic acid-producing compound and a boron reactant.